This invention relates to a process for producing useful concentrated slurries from waste materials.
At present much domestic refuse is collected and taken a considerable distance from the point of collection to an area where it is used as a landfilling material. These filled areas, after allowing for settlement and after providing a layer of topsoil, can be used as playing fields or parkland.
Currently landfill sites in many areas are becoming filled, and new sites difficult to obtain. The generally used alternative to landfilling is incineration which is becoming expensive owing to high capital cost, involves compliance with many stringent environmental requirements and lacks the opportunity for recycling of useful material. With increasing transportation costs, it is desirable to minimize the quantity of material which needs to be transported. Also it is desirable to remove certain constituents of the waste material before disposing of the waste material.
Thus U.S. Pat. No. 2,572,767 (Schlenz) describes a process which involves diluting (with water) and grinding domestic refuse, separating off certain solids like metals, glass and bone, mixing the remainder (which is mainly organic material) with raw sewage sludge, treating the resulting mixture in a digestor where a microorganism produces a combustible gas like methane, burning part of the methane to produce heat for maintaining the digestor at the desired operating temperature, recycling part of the aqueous medium withdrawn from the digestor for use in the aforementioned dilution, and withdrawing a residue from the digestor. That patent, however, is silent regarding the fate of the withdrawn residue. Nonetheless there is disclosed in U.S. Pat. No. 3,838,199 (Coe) a process for recovering feed products from animal waste, in which a sewage sludge is treated in a digestor to produce methane which is burnt to heat the digestor, and in which a slurry withdrawn from the digestor is centrifuged to produce a cake which, when dried, can be used as or in an animal feedstuff.
Also, U.S. Pat. No. 3,847,803 (Fisk) discloses the handling of ground, diluted domestic refuse in which magnetic materials, glass and plastics materials are separated off before the remainder is treated in a digestor which produces a slurry which is centrifuged.
Rather then merely producing an animal feedstuff alone, the present invention has as its object the production of more useful products like boards for insulation, construction or packaging purposes, or fuel; although animal feedstuffs may be produced as a by-product.